The present invention is related, among others, to the geological, mining, particulate production, construction, and quality control industry, and it consists of a method and system for measuring the concentration of different compounds in a particulate material. Its applications include the measurement of the concentration of valuable minerals found in the dust of excavation pits.
For the determination of the concentration of valuable minerals, the commonly used methods in the prior art consider the analysis of samples of dust generated by the drilling of pits that is carried out in an area where the feasibility of exploitation is to be determined. The analysis of dust or debris produced in the drilling of pits is done, after performing the sample selection, either on-site or in a laboratory. The known methods of the prior art for analyzing the concentration of valuable materials use different properties of materials of interest to determine their presence and to what extent they are present.
Generally, the dust generated during the excavation of a pit are removed either manually or mechanically, often in an intrusive manner, and taken to laboratories where they are analyzed using chemical or other similar tests to determine the grade.
From prior art the international patent application WO2008/017.107 is known, entitled ‘Characterization of geological materials by induced thermal response’, which proposes a method and a device for identifying compounds in rocks. The method consists in radiating electromagnetically the rock, preferably with microwaves, to induce a response that manifests itself in temperature changes in the rock, which is then measured using an infrared camera. The infrared image data are analyzed and interpreted in terms of a database. As possible application is mentioned the introduction of this device in pits dug to identify the composition of its walls. However, the application of this method would first suppose the digging of a pit and the measurement would be done at different depths that should be chosen previously.
Another related prior art document is the international patent application WO95/09.962, entitled ‘System for the continuous sampling of soils’, which discloses a system for capturing samples of the material excavated from a pit. Disclosed is a container that can be lowered into the pit hanging from cable and that captures the samples once inside. After the capture, the samples can be raised to be analyzed. As usual in the prior art, the samples have to be handled and transported to a laboratory for analysis and to determine the concentration degree of the ore.
Also known is the publication entitled ‘Enhancing the grade control through borehole geophysics: A case study from the Iron Ore Company of Canada’, Robert L. Gordon, Tim Leriche, Susanne MacMahon; published during the year 2000, available on the Internet, URL: ‘http://www.quantecgeoscience.com/News/ArticlesPublications.php’). This document describes the type of information that can be obtained from the soil to be exploited, in the depth and extension of the terrain, using a probe that descends through the already excavated pits. This probe is equipped with several sensors that determine the magnetic susceptibility, the density and the electrical conductivity among other properties. We mention the relation between the presence of valuable minerals and the measured variables, obtained by comparison with measurements made using traditional methods. The system described in this document includes first making an excavation to obtain a pit and then inserting a probe through this pit, so time, energy, and resources are wasted on the excavation of pits that could be detected as sterile during an early stage.
It is known from prior art the patent WO2006/138632 (A2), entitled ‘Elementary on-line spectroscopic analysis of particles driven by a gas flow’. This document proposes a device through which a gas stream circulates that contains the particles to be analyzed. Inside this device a laser beam turns a small portion of particles into plasma, which emit radiation as they are atomized. This radiation is received and transmitted by an optical fiber to be decomposed into different wavelengths and to generate a measurement of the spectrum. This technique is known as laser induced plasma spectroscopy and it analyzes the radiation emitted by particles that are atomized by a laser beam. The application of this technique requires the use of high-power laser devices capable of converting into plasma a portion of particles whose composition it is desired to be measured. The high-power laser systems impose high energy consumption, make the associated electronics more expensive, and require a careful handling to avoid accidents and deterioration of the other parts of the device to which they belong.
The same patent WO2006/138632 (A2), and the article ‘Improved process control through real-time measurement of mineral content’, of D. Turler, M. Karaca, W. B. Davis, R. Giauque and D. Hopkins, published on Nov. 2, 2001, available online at: ‘http://www.osti.gov/bridge’; propose as an alternative to laser induced plasma spectroscopy to analyze the particle flow by means of fluorescence spectroscopy. In this type of spectroscopy the atoms of the illuminated particles absorb the received energy at a wavelength that allows them to re-emit the radiation in another wavelength; this phenomenon is known as fluorescence. This second wavelength depends on each atom and the analysis of the radiated wavelengths by fluorescence would allow identifying the constituents of the particle flow. The document ‘Improved process control through real-time measurement of mineral content’ proposes the use of X-ray radiation to induce the fluorescence phenomenon on the particles to be analyzed. In fluorescence spectroscopy short wavelengths are used, i.e., highly energy photons, to alter the energy levels of the electrons of the atoms that then will radiate due to fluorescence. The wavelengths of X-rays are in the range between 0.1 nm and 10 nm. X-rays require safe designs that make the implementation, certification, and use more expensive, because they are harmful to living tissue. Additionally, their high penetration level inside standard materials and their ionizing capacity forces complex electronic designs in the process of measuring the spectrum radiated by fluorescence.
Both the patent WO2006/138632 (A2) and the method proposed in the article ‘Improved process control through real-time measurement of mineral content’ assume taking a portion of the material excavated from the borehole, which may induce sampling errors when one considers that, for example, in the case of copper mining, smaller and more volatile particles, and therefore particles more likely to be lost, contain higher concentrations of valuable mineral.
The methods and devices described in the prior art involve a number of fixes and some inefficiencies, such as:
The exposure of the extracted dust and its handling alters its composition due to the loss of valuable particulate material. For example, smaller particles, and thus in general more volatile particles, are those that contain the highest grade in the copper mining industry; on the other hand, in deposits located in the desert the samples may be contaminated by dust that travels with the wind.
The choice of samples of different groups of debris taken from different pits introduces a bias in the ensemble of selected samples when it is not possible to analyze all the pits, a common situation in many types of analysis due to time requirements.
In the methods of laboratories, when samples are taken from the debris produced in the excavation of a pit and a value of grade is assigned to it, a bias is produced by not considering the distribution of the different presence of valuable minerals at different depths inside the same pit.
The analysis of laboratory samples usually restricts the amount of samples capable of being analyzed and delivers results after a certain time, during which it is not possible to take an informed decision about the mineral quality of the soil. This uncertainty is associated with a loss of time or a waste of resources when, as occurs in practice, it is decided to make rock blasting operations before the results of the analysis of grades are available.
The use of a high-energy laser beam for plasma induced emission spectroscopy imposes high energy consumption and designs that must consider the possible and undesired destructive effect of the laser beam on parts of the device that generates it; likewise, safety factors have to be considered in the design. The previously mentioned impositions make the design and the construction more expensive.
The fluorescence spectroscopy techniques require high-energy photon radiation of short wavelength. X-rays with photons that are more energetic than the ones of visible or infrared radiation facilitate the fluorescence but impose restrictions on the design due to their ability to ionize and their high degree of penetration into standard materials. These same characteristics make them harmful to living tissue. These characteristics imply high development, production, certification, and implementation costs. A similar thing happens with other wavelengths commonly used in fluorescence spectroscopy such as gamma rays and UV.
The drawbacks resulting from the application of traditional methods for the determination of the mineral quality of an exploitable soil imply losses due to the inefficient use of time and resources, and due to erroneous estimates produced by bias in the determination of a grade profile in depth and in distribution in the field that has been explored by means of drilling.